We have firstly demonstrated fiber surface enhanced Raman scattering (SERS) sensor based on gold-silver nanoalloys fabricated by a simple and effective photochemical co-reduction method. The nanoalloys are separated into two phases: one phase located in the central circular area of fiber end puts particular emphasis on showing the dispersibility of gold, while the other one in the concentric ring region reflects more on the high enhancement effect of silver. Combining superiorities of gold and silver, fiber SERS sensor based on the biphasic gold-silver nanoalloys shows good reproducibility and high sensitivity. (c) 2012 Elsevier B.V. All rights reserved.